1. Technical Field of the Invention
The present invention relates to a high brightness X-ray generator and a high brightness X-ray generating method by inverse Compton scattering.
2. Description of the Related Art
Synchrotron radiation light (SR light) is an X-ray generated during an orbit change in the case where an orbit of the electron beam accelerated at a speed close to the speed of light is changed by a strong magnet in an annular accelerator (a synchrotron). The SR light is an X-ray source (e.g., an X-ray intensity (a photon number): about 1014 photons/s, a pulse width: about 100 ps), which is incommensurably (103 times or more) intense as compared with the X-ray tube. The SR light is used in fields where a high X-ray intensity is required.
However, a synchrotron radiation light facility in which a synchrotron is used is a large-sized facility in which the synchrotron has a major axis of about 50 m or more and an orbit length reaches 100 m or more, and there is therefore a problem that the facility may not be easily introduced for research or medical treatment.
As means for generating an X-ray by a small-sized device, means capable of obtaining a quasi-monochromatic X-ray arisen from inverse Compton scattering by a collision between an electron beam and a laser beam is known (e.g., Non-Patent Documents 1 and 2).
As small-sized X-ray generating means by inverse Compton scattering, Patent Documents 1, 2 have already been disclosed.
In “Small-Sized X-Ray Generator” of Non-Patent Document 1, as illustrated in FIG. 1, an electron beam 62 accelerated by a small-sized accelerator 61 (an X-band acceleration tube) is allowed to collide with laser 63 to generate an X-ray 64. The electron beam 62 generated by an RF (Radio Frequency) electron gun 65 (a thermal RF gun) is accelerated by the X-band acceleration tube 61, and collides with the pulse laser beam 63. The hard X-ray 64 having a time width of 10 ns is generated by Compton scattering.
In this figure, reference numeral 51 denotes a power source, 52 denotes an a-magnet, 53 denotes a magnet, 54 denotes Q-magnets, 55 denotes a beam dump, 56 denotes a laser unit, 57 denotes a mirror, 58 denotes a lens, 59 denotes a laser dump, 60 denotes a synchronizer, and A denotes a collision point.
This device is miniaturized by using, as an RF, an X-band (11.424 GHz) corresponding to a frequency four times as high as that of an S-band (2.856 GHz) which is generally used in a linear accelerator, and it is predicted that the hard X-ray having, for example, an X-ray intensity (a photon number) of about 1×109 photons/s and a pulse width of about 10 ps will be generated.
In Non-Patent Document 2, as illustrated in FIG. 2, a collision rate is increased in a reaction area by confining and circulating laser light using a plurality of reflection mirrors.
“Laser Inverse Compton Light Generation Device” of Patent Document 1 has an object to generate short-wavelength light such as an X-ray or a y-ray using the effect of inverse Compton scattering.
Thus, in the device of this invention, as illustrated in FIG. 3, a laser inverse Compton light port 72 and a laser beam port 71 are installed at separate positions in a reaction portion 73.
“Laser Light Circulating Device and Laser Light Circulating Method” of Patent Document 2 has an object to concentrate the same laser light at the same laser light focusing point multiple times by confining and circulating the laser light within a predetermined optical path and easily and accurately performing fine adjustment a position of the laser light focusing point, thereby greatly increasing the efficiency of using the laser light.
Thus, as illustrated in FIG. 4, this invention introduces laser light 83 from an outside source, confines the laser light within a circulation path 85 for circulating the laser light, repeatedly passes the laser light through a laser light focusing point 89 within the circulation path, adjusts a position of the laser light focusing point, and concentrates the same laser light at the same laser light focusing point multiple times.
[Non-Patent Document 1]
“Development of Small-Sized Hard X-Ray Source using X-band Linac”, 27-th Linac Technology Research Meeting, 2002, authored by Katsuhiro DOHASHI, et al.
[Non-Patent Document 2]
Yasuo SUZUKI and et al. “A NEW LASER MASS SPECTROMETRY FOR CHEMICAL ULTRATRACE ANALYSIS ENHANCED WITH MULTI-MIRROR SYSTEM (RIMMPA)”, ANALITICAL SCIENCE 2001 Vol. 17 Supplement
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2001-345503 titled “Laser Inverse Compton Light Generation Device”
[Patent Document 2]
Japanese Patent Application Laid-Open No. 2006-344731 titled “Laser Light Circulating Device and Laser Light Circulating Method”
As described above, there have been proposed various devices (e.g., Patent Document 1) that collide laser light with an electron beam to generate an X-ray by inverse Compton scattering. As a technique of increasing the brightness of generated X-rays so far, a technique of circulating and repeatedly colliding an electron ray or laser light in a closed space (e.g., Patent Document 2) has been proposed.
However, the devices in Non-Patent Document 2 and
Patent Document 1 have a problem in that the efficiency of generating an X-ray (i.e., the efficiency of using laser light) is low since the electron beam does not head-on collide with the laser light.
On the other hand, the devices of Non-Patent Document 1 and Patent Document 2 may increase the efficiency of generating an X-ray since the electron beam head-on collides with the laser light. In this case, the amount of X-rays generated, that is, the intensity, is proportional to the number of collisions of the electron beam and the laser light per unit time when an electric current of the electron beam and a photon number of the laser light are uniform.
In the devices of Non-Patent Document 1 and Patent Document 2, the pulse width of the electron beam is, for example, several 100 ns to several 1000 ns, and the frequency is, for example, 10 Hz. The frequency 10 Hz of the electron beam may be easily increased to about 50 Hz by using the same device.
On the other hand, the pulse width of the laser light is, for example, about 10 ns in the case of Nd:YAG laser and the frequency is the same as that of the electron beam, for example, 10 Hz. However, since a facility such as a power source or the like differs greatly, it is usually difficult to increase the frequency of the laser light.
Thus, when aiming at an increase in the brightness of X-rays (i.e., an increase in an X-ray output) in the future, it is possible to increase the number of collisions per unit time by increasing the frequency of an electron beam and laser light, but it is expected that high cost will be required to manufacture a laser unit. It is expected that optical elements such as a mirror and a lens will require custom-made products corresponding to high output power and, of course, the costs will increase.
The present invention has been made to solve the above-described problems. That is, an object of the present invention is to provide a high brightness X-ray generator and a high brightness X-ray generating method capable of promoting an increase in X-ray brightness (i.e., an increase in an X-ray output) while suppressing an excessive increase in the cost of optical elements such as a laser unit, a mirror, and a lens.